Le 8 Mai and the 10-day week

It’s the start of another May holiday weekend in France today: 8 May is Fête de la Victoire, the anniversary of VE Day, Victory day in Europe in the Second World War.

It’s another, not quite so famous anniversary. On May 8 1790, the French National Assembly decided to introduce the metric system – and the 10-day week.

A 10-hour clock near the beginning of Fritz Lang's "Metropolis", reflecting the improved efficiency of a futuristic industrial society

The original metric system was intended to be used with the time units of the new French Republican calendar, which tried to do its best to decimalise time itself.

A year still had 12 months, but now they were divided into three 10-day weeks (“décades”). The tenth day (“décadi”) replaced Sunday as the day of rest and festivity, so you can see why it started to have problems from day 1.0.

Each day was divided into 10 hours, each hour into 100 decimal minutes and each decimal minute had 100 decimal seconds.

So an hour was over twice as long as a conventional hour, a minute was a bit longer than a conventional minute, and a second was slightly shorter than a conventional one.

Napoleon officially abolished the calendar in 1806, about 12 years after its introduction, though it made a brief comeback during the Paris Commune of 1871. Read more about the revolutionary calendar.

The metric system

Thankfully, though, the metric system of weights and measures did survive. It wa a completely new system, because the French revolutionary government figured that it would have less resistance than trying to standardise loads of existing ones between countries.

I think it fair to say that it changed the nature of science, commerce, international trade and tons (or is that tonnes?) more stuff as well.

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